Self-centering chucks are known, which comprise a basic body consisting of a steel casting with guide grooves, a threaded spindle, which is mounted rotatably about its longitudinal axis and has a right-handed external thread in a first axial area and a left-handed external thread in a second axial area and is provided centrally with a groove surrounding the circumference of the threaded spindle, two slides screwed onto an external thread each of the threaded spindle with a clamping jaw each arranged in the head area, which are guided movably in the axial direction with sliding blocks screwed onto the slides in the guide grooves of the basic body and on the threaded spindle, wherein the threaded spindle is centered in a central piece, which is arranged between the slides and against which the two slides are to be clamped, and can be fixed and locked at the basic body and at the central piece by fastening means guided in the groove, so that rotation of the threaded spindle leads to an axial motion of the slides with the clamping jaws towards or away from each other.
One problem of the self-centering chucks of the class described is that the clamping jaws made integrally in one piece with the top side have only one clamping surface each suitable for clamping only. Only two clamping jaws arranged opposite each other with their clamping surface are suitable for fixing the position of workpieces. The outer surfaces of the clamping jaws have predominantly a material-saving shape, but they have no functional significance. Based on this, the clamping path between the clamping jaws remains very limited. Furthermore, the slides are equipped each only with a right-handed or left-handed thread, and they can therefore be screwed only onto the right-handed or left-handed thread of the spindle. In addition, the sliding blocks screwed to the slides may become loose and tilt, which requires time-consuming and labor-intensive maintenance in view of the required precision.